1. Field of the Invention
The application relates to a method utilized in a wireless communication system and a communication device thereof, and more particularly, to a method of handling proximity information transmission in a wireless communication system and a related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
In the LTE system, a UE supporting a closed subscriber group (CSG) feature can transmit proximity information to the network for triggering inbound mobility (namely handover) to a CSG/hybrid cell. The UE supporting the CSG feature has a CSG whitelist which contains one or more CSG identities associated with CSG cells on which the UE is allowed access. The CSG cell is associated with a small coverage base station which may be deployed for magnificent advantages, such as the high bandwidth wireless internet access in the home and office, and efficient and cost-effective capacity solution for indoor coverage, whereas the hybrid cell is accessed as a CSG cell by a UE whose CSG whitelist contains a CSG identity of the cell and as a normal cell by all other UEs.
As to an operation of the inbound mobility, the proximity information is sent to the network (i.e. the E-UTRAN, an eNB, or a base station) when the UE detects that it is close to a CSG cell in its CSG whitelist. The network configures the UE with a measurement configuration including a measurement gap if needed after the proximity information is received. Meanwhile, the UE reads the system information of the detected CSG cell for obtaining the CSG identity of the detected CSG cell, and checks whether the CSG identity is in the CSG whitelist. If the CSG identity is in the CSG whitelist indeed, the UE performs the measurement to the detected CSG cell, so as to generate a measurement report to the network for a handover preparation. Thus, the network determines whether to handover the UE to the CSG cell according to the measurement report.
In addition, the UE is allowed to transmit the proximity information to the network when the network indicates that the inbound mobility to CSG/hybrid cells is support. For example, the UE initiates an RRC connection reconfiguration request procedure to transmit the proximity information to the network in an “RRCConnectionReconfigurationRequest” message when an “RRCConnectionReconfiguration” message, which includes a field of “inboundHO-Support” indicating that a first eNB presently serving the UE supports the inbound mobility to CSG/hybrid cells, is received from the network. However, the UE may meet a radio link failure and performs an RRC connection re-establishment procedure to a second eNB. Meanwhile, the UE detects that it is close to a CSG cell in the CSG whitelist, and sends the “RRCConnectionReconfigurationRequest” message to the second eNB. Nevertheless, the second eNB may not support the inbound mobility to CSG/hybrid cells. The “RRCConnectionReconfigurationRequest” message may confuse the second eNB or make the second eNB system failure because the second eNB is unable to process the “RRCConnectionReconfigurationRequest” message.
Furthermore, the abovementioned situation may occur in a universal mobile telecommunications system (UMTS). For example, the UE provides a serving radio network controller (SRNC) with the proximity information when it is near a CSG/hybrid cell whose CSG identity is in the UE's CSG whitelist. Due to similar behavior in the UMTS system, the foregoing problems arise as well.